1. Field of the Invention
The present invention relates to a layer member forming method which is suitable for use in the fabrication of various electronic devices of the type having an insulating, protecting, conductive, semiconductor or like layer member formed on a substrate member.
2. Description of the Prior Art
Heretofore there has proposed a method for forming such a layer member on a substrate member through use of a photo CVD or plasma CVD process.
According to the method utilizing the photo CVD technique, the substrate is placed in a reaction chamber provided with a light transparent window and a reactive gas mixture, which contains at least a gas of a material for the formation of the layer member desired to obtain, is introduced into the reaction chamber. Then light is introduced into the reaction chamber through the light transparent window thereof by which the reactive gas mixture introduced thereinto is excited for vapor-phase decomposition and the material for the layer is deposited on the substrate member.
With the method utilizing the plasma CVD technique, the substrate is placed in a reaction chamber and a reactive gas mixture, which contains a gas of a material for the formation of the layer, is introduced into the reaction chamber. In the reaction chamber the reactive gas mixture is excited into a plasma by glow discharge or electron cyclotron resonance for vapor-phase decomposition by high frequency electric power so that the material for the layer is deposited on the substrate.
With the photo CVD process, since the material gas resulting from the vapor-phase decomposition of the photo-excited reactive gas is not accelerated, it is possible to form the layer on the substrate with substantially no damage inflicted on the substrate surface. On this account the layer can easily be formed without containing the material forming the substrate surface or without introducing into the substrate surface the material forming the layer, without developing any undesirable interface level between the layer and the substrate and without applying any internal stress to the layer and the substrate. Furthermore, since the photo-excited material gas has a characteristic to spread on the surface of the substrate member, the layer can be deposited in close contact with the substrate even if the substrate surface is uneven.
Accordingly, the use of the photo CVD technique permits easy formation of the layer of desired characteristics, without causing any damages to the substrate surface, even if the substrate has an uneven surface.
With the photo CVD process, however, since the photo-excited material gas is not accelerated toward the substrate, the deposition rate of the layer is lower than in the case of employing the plasma CVD technique. Therefore, the photo CVD process takes much time for forming the layer as compared with the plasma CVD process. Furthermore, the material for the layer is deposited as well on the light transparent window during the formation of the layer, causing a decrease in the light transmittivity of the window as the deposition proceeds. Therefore, the layer cannot be formed to a large thickness. For instance, in the case of forming a silicon nitride layer, it is difficult, in practice, to deposit the layer to a thickness greater than 1000 A. Moreover, difficulties are encountered in forming a silicon layer to a thickness greater than 200 A, a silicon oxide (SiO.sub.2), or aluminum nitride (AlN) layer to a thickness greater than 3000 A, a silicon carbide (Si.sub.sC.sbsb.1-x, where 0&lt;x&lt;1) layer to a thickness greater than 500 A and a germanium silicide (Si.sub.x Ge.sub.1-x, where 0&lt;x&lt;1) or metal silicide (SiM.sub.x, where M is metal such as Mo, W, In, Cr, Sn Ga or the like and 0&lt;X.ltoreq.4) layer to a thickness greater than 100 to 200 A.
With the plasma CVD process, since the material gas resulting from the vapor decomposition of the reactive gas excited by electric power can be accelerated toward the substrate, the deposition rate of the layer is higher than in the case of using the photo CVD process. Therefore, the layer can be formed on the substrate in a shorter time than is needed by the photo CVD technique. Furthermore, even if the material for the layer is deposited on the interior surface of the reaction chamber as well as on the substrate, no limitations are imposed on the excitation of the reactive gas by electric power. Consequently, the layer can easily be formed to a desired thickness on the substrate.
With the plasma CVD technique, however, since the material gas excited by electric power is accelerated by an electric field, it is difficult to deposit the layer on the substrate without causing damage to its surface. On account of this, the layer contains the material forming the substrate surface, or the substrate surface contains the material forming the layer. Moreover, an interface level is set up between the layer and the substrate and internal stresses are applied to the layer and the substrate.
Besides, in the case of employing the plasma CVD technique, since the excited material gas is accelerated by an electric field and its free running In the reaction chamber is limited, there is the possibility that when the substrate surface is uneven, the layer cannot be formed in close contact therewith, that is, the layer cannot be deposited with desired characteristics.